High molecular weight biopolymers such as fungal glucans and microbial polysaccharides are produced by fermentation. Upon completion of fermentation, a complex broth results. To harvest biopolymers from the broth, typically the fermentation broth is either recovered, diluted, and dried without additional handling, or processed further to remove a substantial quantity of the biomass and then dried. In both instances, the polysaccharide-containing broth is homogenized, diluted (two to three fold) and the polysaccharide harvested by direct precipitation with one-half to two volumes of alcohol. In order to effect complete recovery of the polysaccharide, this mixture can be cooled (<10° C.) and allowed to stand for several hours. The precipitated materials are then recovered from the mixture with a screen or sieve, dried in an oven, milled, and packaged. The final product of the native or processed polysaccharide broth is a dry, flowable powder.
While the dry product form is easy to transport and handle, the harvesting process suffers from numerous drawbacks. The most significant drawbacks stem from the handling, processing and recovery of the large quantities of alcohol. The process is costly, and not economical without a nearly complete recovery of the alcohol. The dried powders are also difficult to rehydrate. The drying processes may negatively affect some of the physiochemical attributes. For example, entanglement of the biopolymers during precipitation and drying can lead to clipping of the polymer and the generation of lower molecular weight species during the milling and rehydration processes. This problem is amplified if lengthy high shear agitation is required to hydrate the polymer. These events can reduce the functionality and ultimately the value of the biopolymer.
Other drying procedures, including drum drying and spray drying, have been investigated but not commercialized. It is believed that, in general, the practical and functional limitations of these drying technologies as well as the economics and the final product attributes significantly reduce the utility of these systems.
Alternative recovery processes such as membrane filtration have also been proposed and developed to concentrate the fermentation broth. The product of the membrane concentration processes, for example, is a 90–95% aqueous concentrate or gel. While this process addresses some of the liabilities of the precipitation process, the concentrate (or gel) product form cannot be efficiently or economically transported, nor handled as a standard material in most industrial applications.
Still other precipitation and recovery methods are known in the art; however, none of these offers any significant advantage to the standard alcohol precipitation procedure. Consequently, the need or preference for a dry product coupled with the cost and inherent limitations of the alcohol precipitation procedure has limited the development and application of these and related functional biomaterials in an array of industrial applications.
A significant drawback to many prior art-drying processes is that the process often kills live microorganisms that are present in an aqueous medium, such as a fermentation broth. For instance, lactic acid bacteria in a whole both or a concentrated cell slurry are not readily amenable to drying to yield viable dry bacteria. When high yields of viable dry cells are desired, the most common way to dry such cells in commercial practice is to lyophilize the cells in the presence of excipients. Lyophilization is expensive, and the lyophilized cells ordinarily cannot be stored in an open package at room temperature. Such cells often are stored within an oxygen barrier packaging material, often with an oxygen scavenging material or in gel form. In addition, cell availability generally degrades after storage at room temperature for more than a few weeks. These drawbacks have hindered the use of lactic acid bacteria, especially probiotic use in animal feeds.
Another problem in the art relates to the drying of oily materials. Oils, lipids and related biomolecules often need to be extracted using solvents from fermentation propagated cells such as algae and related microorganisms. Prior to performing the solvent extraction, however, the cells need to be concentrated, i.e., the broth “dewatered,” in order to attain a cost-effective extraction and process. In the absence of a concentration step, however, the quantity of solvent required and costs associated therewith can be very high. Typically, this is now achieved by concentrating the cells either by centrifugation or filtration or drying the concentrated cells by spray drying and then extracting the spray-dried cells. Although possible, this is often not practical or very feasible especially in applications where the cells are “leaky” or fragile and exuding oily materials. It is known that the presence of oily materials complicates drying by most known technologies.
The invention seeks to provide, in preferred embodiments, a drying operation that is inexpensive and produces a dry flowable powder with good handling and packaging characteristics that can be formulated to retain the functional attributes of the native biomolecule.